This invention relates to a method and apparatus for automatically winding toroidal coils and, in particular, to a method and apparatus for automatically winding a length of wire on a ring-shaped core, with the wire passing through a central aperture of the core. As used herein, the term "ring-shaped core" means an article having a closed curve cross-section of a toroid such as a toroidal core or any one of hollow cross-sections.
Methods for winding toroidal coils with a conventional automatic winding machine come into three general categories described below.
In the first method, three rollers are abutted to the peripheral surface of a core to support it rotatably and the wire of a predetermined length is contained within a shuttle in a winding machine. The shuttle carrying a length of wire travels through the central aperture of the core and the wire is drawn out of the shuttle through an opening provided in it. This method is, however, time consuming and ineffective due to the necessity of preparing the wire within the shuttle. In addition, the wire may be rubbed against the periphery of the opening. This may result in some damages on an insulating layer of the wire. Another disadvantage is that the shuttle passes through the central aperture of the core, which restricts the application of it only to relatively large cores. Furthermore, smooth rotation of the core becomes more difficult as the winding proceeds and thus this method sometimes has a trouble in lap winding of the wire.
The second method is directed to a hook-winding of the wire, in which two steps are repeated: to pass the wire of a predetermined length over a surface of the core at one side thereof and to catch the wire with a hook extending from the other side of the core through the central aperture thereof. This method is seriously disadvantageous in that the wire is rubbed against the hook, causing an insulating layer to be damaged.
On the other hand, the third method provides a shuttleless winding machine that requires no hook as well. Instead, the third method requires multiple turning of the core. One end (leading end) of the wire is passed through the central aperture of the core and is extended in the core axial direction. The core is then turned through 180.degree. on a diametrical axis thereof together with the other end (tailing end) of the wire. This turn allows the wire to be laid on the outer periphery of the core. Subsequently, the leading end is again passed through the central aperture to lay the wire on the inner periphery of the core and thus one loop is wound about the core. These steps are repeated until enough wire is wound into a coil. In this event, the core is rotated about its axis by a winding pitch before each turn or reverse through 180.degree.. This rotation is achieved using a pair of core turning clamps. The core turning clamps hold less than the respective halves of the core at the opposing sides thereof and are capable of turning the core in one direction on the diametrical axis thereof. The rotation axes of the core turning clamps cross each other at an angle of the winding pitch. Accordingly, movement of the core turning clamps results in rotation of the core by the winding pitch.
In this method, lap winding can be made by changing the cross angle of the core turning clamps from plus to minus or vice versa. Such rotation which relies on changing the holding position may create a problem, especially when each clamp holds the core being covered with the first layer of the wire upon lap winding. Thus, this method is also disadvantageous because of potential problems which may occur in the subsequent winding.